Screw Compressor System for a Utility Vehicle

ABSTRACT

A screw compressor system for a utility vehicle has at least one screw compressor, at least one screw compressor drive and at least one control and/or regulation unit. The control and/or regulation unit is connected to the screw compressor drive and is designed and configured such that it monitors, when the screw compressor is in operation, the ratio of idle time and switched on time of the screw compressor drive and this ratio controls and regulates to a predetermined range.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a screw compressor system for a utility vehicle, having at least one screw compressor with at least one open-loop and/or closed-loop control unit for the open-loop and/or closed-loop drive control of the screw compressor.

Screw compressors for utility vehicles are already known from the prior art. Such screw compressors are used to provide the compressed air required for the brake system of the utility vehicle, for example.

In this context, in particular oil-filled compressors, in particular also screw compressors, are known, in the case of which it is necessary to regulate the oil temperature. This is generally realized by virtue of an external oil cooler being provided which is connected to the oil-filled compressor and to the oil circuit via a thermostat valve. Here, the oil cooler is a heat exchanger which has two mutually separate circuits, wherein the first circuit is provided for the hot liquid, that is to say the compressor oil, and the second circuit is provided for the cooling liquid. As cooling liquid, use may for example be made of air, water mixtures with an antifreeze, or another oil.

This oil cooler must then be connected to the compressor oil circuit by means of pipes or hoses, and the oil circuit must be safeguarded against leakage.

This external volume must furthermore be filled with oil, such that the total quantity of oil is also increased. The system inertia is thus increased. Furthermore, the oil cooler must be mechanically accommodated and fastened, either by means of brackets situated in the surroundings or by means of a separate bracket, which necessitates additional fastening means and also structural space.

U.S. Pat. No. 4,780,061 has already disclosed a screw compressor with an integrated oil cooling arrangement.

Furthermore, DE 37 17 493 A1 discloses a screw compressor installation which is arranged in a compact housing and which has an oil cooler on the electric motor of the screw compressor.

A generic screw compressor is already known for example from DE 10 2004 060 417 B4.

It is the object of the present invention to advantageously further develop a screw compressor system of the type mentioned in the introduction, in particular such that the open-loop and/or closed-loop drive control of the screw compressor can be made simpler and reliable.

This object is achieved according to the invention by a screw compressor system for a utility vehicle equipped with at least one screw compressor, at least one screw compressor drive, and at least one open-loop and/or closed-loop control unit. The open-loop and/or closed-loop control unit is connected to the screw compressor drive, wherein the open-loop and/or closed-loop control unit is designed and configured such that, during the operation of the screw compressor, said open-loop and/or closed-loop control unit monitors the ratio of idle time and activated time of the screw compressor drive and adjusts said ratio to a predefined range by open-loop and/or closed-loop control.

The invention is based on the underlying concept that the ratio of idle time and activated time also significantly co-determines the temperature of the screw compressor. Depending on the type of construction of the screw compressor, adjusting the ratio of idle time and activated time to a predefined range by open-loop control is sufficient to be able to keep the screw compressor in a very narrow operating temperature range. The intermeshing screws and the oil conducted through the screw compressor and the compressed air lead to generation of heat, such that, through corresponding selection of the ratio of idle time and activated time of the screw compressor drive, it is also simultaneously possible for the heat of the screw compressor to be adjusted by open-loop and/or closed-loop control, that is to say set.

For example, provision may be made for the open-loop and/or closed-loop control unit to be a constituent part of the screw compressor system, that is to say either of the screw compressor or of the screw compressor drive. In this way, a compact construction is formed, and it is not necessary to resort to external components.

It is however basically also conceivable for the open-loop and/or closed-loop control unit to be a constituent part of an air treatment system of the utility vehicle. Here, a corresponding controller is already provided, which can easily be jointly utilized.

It is also conceivable for the open-loop and/or closed-loop control unit to be a constituent part of an engine or vehicle controller of the utility vehicle. Here, too, it would be possible to be able to resort to an already existing component of the utility vehicle.

It is however basically also conceivable for the open-loop and/or closed-loop control unit to be in the form of a separate open-loop and/or closed-loop control unit. This permits, for example, easy installation and also an easy exchange or easy upgrade.

Provision may furthermore be made whereby the range is selected such that a ratio of idle time to activated time is present in which the activated time amounts to approximately 20 to 50%, in particular >30%. This ratio of idle time to activated time with an activated time of between approximately 20% and 40%, in particular of >30%, has proven to be relatively expedient in order to be able to keep the operating temperature substantially constant. A further resulting advantage is that, through ensuring a ratio of idle time to activated time with an activated time of >30%, the operating temperature remains high enough to also reliably prevent moisture formation or condensation in the interior of the screw compressor.

Provision may furthermore be made whereby the open-loop and/or closed-loop control unit is designed and configured so as to influence the rotational speed of the screw compressor drive such that the ratio of idle time and activated time of the screw compressor drive is kept in the predefined range. It is substantially assumed here that a certain compressed-air quantity is to be provided over the entire running time of the screw compressor, and that, through the definition or limitation or increase of the rotational speed of the screw compressor drive over the overall running time, while maintaining constant compressed-air production, the ratio of idle time and activated time of the screw compressor drive can also be influenced and thus kept in the predefined range.

In particular, provision may be made whereby the open-loop and/or closed-loop control unit is designed and configured so as to keep the rotational speed of the screw compressor drive above a minimum rotational speed at all times. This possibility of keeping the rotational speed above a minimum rotational speed is based on the underlying concept that, above a certain minimum rotational speed, a limitation of the power loss occurs for the first time, and the screw compressor drive requires less energy to generate a particular quantity of compressed air. In other words, the efficiency of the screw compressor can be improved overall in this way. For example, it is known that the power loss can greatly increase below minimum rotational speeds of approximately 1500 to 2500 revolutions per minute, such that an undershooting of these minimum rotational speeds should be avoided where possible.

Further details and advantages of the invention will now be discussed in more detail on the basis of an exemplary embodiment illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional drawing through a screw compressor according to the invention; and

FIG. 2 shows a schematic drawing of the screw compressor system according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in a schematic sectional illustration, a screw compressor 10 in the context of an exemplary embodiment of the present invention.

The screw compressor 10 has a fastening flange 12 for the mechanical fastening of the screw compressor 10 to an electric motor (not shown in any more detail here).

What is shown, however, is the input shaft 14, by which the torque from the electric motor is transmitted to one of the two screws 16 and 18, specifically the screw 16.

The screw 18 meshes with the screw 16 and is driven by means of the latter.

The screw compressor 10 has a housing 20 in which the main components of the screw compressor 10 are accommodated.

The housing 20 is filled with oil 22.

At the air inlet side, an inlet connector 24 is provided on the housing 20 of the screw compressor 10. The inlet connector 24 is in this case designed such that an air filter 26 is arranged at said inlet connector. Furthermore, an air inlet 28 is provided radially on the air inlet connector 24.

In the region between the inlet connector 24 and the point at which the inlet connector 24 joins to the housing 20, there is provided a spring-loaded valve insert 30, which is designed here as an axial seal.

This valve insert 30 serves as a check valve.

Downstream of the valve insert 30, there is provided an air feed channel 32 which feeds the air to the two screws 16, 18.

At the outlet side of the two screws 16, 18, there is provided an air outlet pipe 34 with a riser line 36.

In the region of the end of the riser line 36, there is provided a temperature sensor 38 by means of which the oil temperature can be monitored.

Also provided in the air outlet region is a holder 40 for an air deoiling element 42.

In the assembled state, the holder 40 for the air deoiling element has the air deoiling element 42 in the region facing toward the base (as also shown in FIG. 1).

Also provided, in the interior of the air deoiling element 42, is a corresponding filter screen or known filter and oil separator devices 44, which will not be specified in any more detail.

In the central upper region in relation to the assembled and operationally ready state (that is to say as shown in FIG. 1), the holder for the air deoiling element 42 has an air outlet opening 46 which leads to a check valve 48 and a minimum pressure valve 50. The check valve 48 and the minimum pressure valve 50 may also be formed in one common combined valve.

The air outlet 51 is provided downstream of the check valve 48.

The air outlet 51 is generally connected to correspondingly known compressed-air consumers.

In order for the oil 22 that is situated and separated off in the air deoiling element 42 to be returned into the housing 20 again, a riser line 52 is provided which has a filter and check valve 54 at the outlet of the holder 40 for the air deoiling element 42 at the transition into the housing 20.

A nozzle 56 is provided, downstream of the filter and check valve 54, in a housing bore. The oil return line 58 leads back into approximately the central region of the screw 16 or of the screw 18 in order to feed oil 22 thereto again.

An oil drain screw 59 is provided in the base region, in the assembled state, of the housing 20. By means of the oil drain screw 59, a corresponding oil outflow opening can be opened, via which the oil 22 can be drained.

Also provided in the lower region of the housing 20 is the attachment piece 60 to which the oil filter 62 is fastened. Via an oil filter inlet channel 64, which is arranged in the housing 20, the oil 22 is conducted firstly to a thermostat valve 66.

Instead of the thermostat valve 66, it is possible for an open-loop and/or closed-loop control device to be provided by means of which the oil temperature of the oil 22 situated in the housing 20 can be monitored and set to a setpoint value.

Downstream of the thermostat valve 66, there is then the oil inlet of the oil filter 62, which, via a central return line 68, conducts the oil 22 back to the screw 18 or to the screw 16 again, and also to the oil-lubricated bearing 70 of the shaft 14. Also provided in the region of the bearing 70 is a nozzle 72, which is provided in the housing 20 in conjunction with the return line 68.

The cooler 74 is connected to the attachment piece 60.

In the upper region of the housing 20 (in relation to the assembled state), there is situated a safety valve 76, by means of which an excessively high pressure in the housing 20 can be dissipated.

Upstream of the minimum pressure valve 50, there is situated a bypass line 78, which leads to a relief valve 80. Via said relief valve 80, which is activated by means of a connection to the air feed 32, air can be returned into the region of the air inlet 28. In this region, there may be provided a ventilation valve (not shown in any more detail) and also a nozzle (diameter constriction of the feeding line).

Furthermore, approximately at the level of the line 34, an oil level sensor 82 may be provided in the outer wall of the housing 20. Said oil level sensor 82 may for example be an optical sensor, and may be designed and configured such that, on the basis of the sensor signal, it can be identified whether the oil level during operation is above the oil level sensor 82 or whether the oil level sensor 82 is exposed, and thus the oil level has correspondingly fallen.

In conjunction with this monitoring, it is also possible for an alarm unit to be provided which outputs or transmits a corresponding error message or warning message to the user of the system.

The function of the screw compressor 10 shown in FIG. 1 is as follows.

Air is fed via the air inlet 28 and passes via the check valve 30 to the screws 16, 18, where the air is compressed. The compressed air-oil mixture, which, having been compressed by a factor of between 5 and 16 downstream of the screws 16 and 18, rises through the outlet line 34 via the riser pipe 36, is blown directly onto the temperature sensor 38.

The air, which still partially carries oil particles, is then conducted via the holder 40 into the air deoiling element 42 and, if the corresponding minimum pressure is attained, passes into the air outlet line 51.

The oil 22 situated in the housing 20 is kept at operating temperature via the oil filter 62 and possibly via the heat exchanger 74.

If no cooling is necessary, the heat exchanger 74 is not used and is also not activated.

The corresponding activation is performed by means of the thermostat valve 66. After purification in the oil filter 62, oil is fed via the line 68 to the screw 18 or to the screw 16, and also to the bearing 70. The screw 16 or the screw 18 is supplied with oil 22 via the return line 52, 58, and the purification of the oil 22 takes place here in the air deoiling element 42.

By means of the electric motor (not shown in any more detail), which transmits its torque via the shaft 14 to the screw 16, which in turn meshes with the screw 18, the screws 16 and 18 of the screw compressor 10 are driven.

By means of the relief valve 80 (not shown in any more detail), it is ensured that the high pressure that prevails for example at the outlet side of the screws 16, 18 in the operational state cannot be enclosed in the region of the feed line 32, and that, instead, in particular during the start-up of the compressor, there is always a low inlet pressure, in particular atmospheric pressure, prevailing in the region of the feed line 32. Otherwise, upon a start-up of the compressor, a very high pressure would initially be generated at the outlet side of the screws 16 and 18, which would overload the drive motor.

FIG. 2 shows, in a schematic illustration, a screw compressor system 100 according to the invention, having the screw compressor 10 shown in FIG. 1 and an open-loop and closed-loop control unit 110.

Here, the open-loop and closed-loop control unit 110 is formed as a constituent part of the screw compressor system 100.

Provision may however basically be made for the open-loop and closed-loop control unit 110 to be formed as a constituent part of an air treatment system of the utility vehicle, as a constituent part of an engine or vehicle controller of the utility vehicle, or as a separate open-loop and closed-loop control unit 110.

Here, the open-loop and closed-loop control unit 110 is designed and configured such that, during the operation of the screw compressor 10, said open-loop and closed-loop control unit monitors the ratio of idle time and activated time of the screw compressor drive for driving the screws 16 and 18 and adjusts said ratio to a predefined range by open-loop and/or closed-loop control.

Here, said range is selected such that a ratio of idle time to activated time is present in which the activated time amounts to >30%. In particular, a range is selected here which lies between 30 and 50% activated time, such that the idle time thus lies between 50% and 70% and the activated time is approximately 30 to 50%.

In the case of an activated time of approximately 30%, the idle time consequently amounts to approximately 70%.

In order to be able to also keep the ratio of idle time to activated time correspondingly constant, the open-loop and closed-loop control unit 110 is furthermore designed and configured so as to jointly influence the rotational speed of the screw compressor drive.

It is ensured here that, by means of a reduction and/or increase of the rotational speed of the screw compressor drive, the desired compressed-air quantity is provided by the screw compressor 10 over the entire operating duration, but the ratio of idle time and activated time is maintained.

For economical and energy-efficient operation, it is also the case here that the rotational speed is kept above a minimum rotational speed at all times by means of the open-loop and closed-loop control unit 110.

This is based on the realization that, below the minimum rotational speed, the specific energy consumption of the screw compressor drive (that is to say for example the energy quantity required to compress one cubic meter (m³) of air) increases very greatly. In other words, excessively high power losses or high losses are thus prevented from occurring.

By virtue of the ratio of idle time to activated time being kept constant, it is thus achieved overall that, over the entire operating duration, the screw compressor 10 can be kept at an operating temperature in a relatively constant manner.

By virtue of the compressor being kept at operating temperature over the entire operating duration, condensation is reliably prevented from occurring in the housing 20 of the screw compressor 10.

Owing to the constant operating temperature and the fact that the screw compressor 10 is kept at operating temperature, condensation in the housing 20 is reliably avoided.

LIST OF REFERENCE SIGNS

-   10 Screw compressor -   12 Fastening flange -   14 Input shaft -   16 Screws -   18 Screws -   20 Housing -   22 Oil -   24 Inlet connector -   26 Air filter -   28 Air inlet -   30 Valve insert -   32 Air feed channel -   34 Air outlet pipe -   36 Riser line -   38 Temperature sensor -   40 Holder for an air deoiling element -   42 Air deoiling element -   44 Filter screen or known filter or oil separation devices -   46 Air outlet opening -   48 Check valve -   50 Minimum pressure valve -   51 Air outlet -   52 Riser line -   54 Filter and check valve -   56 Nozzle -   58 Oil return line -   59 Oil drain screw -   60 Attachment piece -   60 a Outer ring -   60 b Inner ring -   62 Oil filter -   64 Oil filter inlet channel -   66 Thermostat valve -   68 Return line -   70 Bearing -   72 Nozzle -   76 Safety valve -   78 Bypass line -   80 Relief valve -   82 Oil level sensor -   100 Screw compressor system -   110 Open-loop and closed-loop control unit 

1-8. (canceled)
 9. A screw compressor system for a utility vehicle, comprising: at least one screw compressor; at least one screw compressor drive; and at least one open-loop and/or closed-loop control unit, wherein the open-loop and/or closed-loop control unit is connected to the screw compressor drive, the open-loop and/or closed-loop control unit is configured such that, during operation of the screw compressor, said open-loop and/or closed-loop control unit monitors a ratio of idle time and activated time of the screw compressor drive and adjusts said ratio to a predefined range by open-loop and/or closed-loop control.
 10. The screw compressor system as claimed in claim 9, wherein the open-loop and/or closed-loop control unit is a constituent part of the screw compressor system.
 11. The screw compressor system as claimed in claim 9, wherein the open-loop and/or closed-loop control unit is a constituent part of an air treatment system of the utility vehicle.
 12. The screw compressor system as claimed in claim 9, wherein the open-loop and/or closed-loop control unit is a constituent part of an engine or vehicle controller of the utility vehicle.
 13. The screw compressor system as claimed in claim 9, wherein the open-loop and/or closed-loop control unit is a separate open-loop and/or closed-loop control unit.
 14. The screw compressor system as claimed in claim 9, wherein the predefined range is selected such that a ratio of idle time to activated time is present in which the activated time amounts to approximately 20-40%.
 15. The screw compressor system as claimed in claim 9, wherein the predefined range is selected such that a ratio of idle time to activated time is present in which the activated time amounts to approximately more than 30%.
 16. The screw compressor system as claimed in claim 9, wherein the open-loop and/or closed-control loop unit is configured so as to influence the rotational speed of the screw compressor drive such that the ratio of idle time and activated time of the screw compressor drive is kept in the predefined range.
 17. The screw compressor system as claimed in claim 16, wherein the open-loop and/or closed-loop control unit is configured so as to keep the rotational speed of the screw compressor drive above a minimum rotational speed at all times. 